Electrodermal activity

Electrodermal activity (EDA) is one of the most studied psychophysiological markers of the various functions regulated by the autonomic nervous system and it has been applied in psychophysiological research for over a 100 years (Boucsein 2012). EDA is an indicator of the sympathetic activity of the autonomic nervous system, which is associated with emotion, cognition, and affection (e.g. Critchley 2002). 

EDA reflects the functions of the autonomic nervous system (ANS) and is often used in evaluation of mental states, e.g. short- and long-term stress. The physiological stress reaction is strongly related to the sympathetic nervous system. Because skin conductivity is mainly a result of sweat gland activity solely controlled by the sympathetic nervous system, EDA is one of the most direct methods to measure the stress related ANS responses.

Where to measure to get an accurate signal

When the eccrine sweat glands are innervated by the sympathetic nervous system activation they push sweat to the surface of the skin. Measuring electricity from the surface of the skin requires this moisture to act as a conductor. The density of the eccrine sweat glands is the highest on the palmar and sole skin, making a finger ring an efficient and easy way to measure EDA.

Does electrodermal activity correlate with the heart rate variability (HRV)?

Electrodermal activity is purely an indication of the sympathetic nervous system activation. The parameters the HRV tell of both the sympathetic and parasympathetic activation. 

The sympathetic nervous system activates the fight-or-flight response, also called an acute stress response. Electrodermal activity is more sensitive to emotional and cognitive stress than the HRV.

Electrodermal activity is also known as galvanic skin response (GSR) or skin conductance response (SCR).

The EDA raw signal is a continuously changing curve with no repeating pattern. Frequency and amplitude of the curve change according to the sympathetic nervous system activity.